Radiocircuits



` Jan. 1, 1929 W. MEDVED RADIOCIRCUITS Filed Nov. 27, 1926 U i: l E" b. s

.All H pl n# Raw glu/miam Sudam? Patented `lan. 1, 1929.

WALTER Mnnvnn, or CANTON, oHio,

RADIOGIRCUITS.

Application filed November 27, 1926. SerialiNo. 151,097.

My invention relates to radio circuits including vacuum tubes in combination with a source of power, resistances, inductances, and capacities, and more particularly to circuits including a primary coil connected between the plate of a vacuum tube and a power terminal, and the primary coil having associated therewith a secondary coil, whereby the primary coil and the secondary coil may constitute a radio frequency transformer, the secondary coil being connected in a usual manner with one or more vacuum tubes, transformers and the like for further amplifying and/or detecting the currents which may have been induced in the first mentioned secondary by the first mentioned primary.

The aforesaid first mentioned vacuum tube may be designated as a radio frequency tube, and the first mentioned primary and secondary may constitute a radio frequency transformer therefor.

Radio frequency currents may be passed through the first mentioned radio frequency vacuum tube by any well known means as from an antenna or a loop.

lt has been found that when such a radio frequency vacuum tube is operated in the usual manner, that the desired radio frequency currents are passed therethrough at the greatest eiiiciency when the tube is just below the oscillation point.

It has been very difficult however to maintain the tube at the desired condition just below the oscillation point by means heretofore known, it being the usual experience that the aforesaid radio frequency tube will suddenly commence to oscillate and thereby interfere with the passage of the desired radio frequency currents through the tube and into the aforesaid primary.

l/Vhen such a radio frequency tube and radio frequency transformer' is combined with other tubes and transformers to form a radio frequency broadcast receiving apparatus, this tendency of the tubes to osci late, prevents the receiving apparatus from being adjusted for passing the desired radio frequency currents therethrough at highest efficiency, whereby the relatively small energ impressed upon the receiving apparatus by a distant broadcast transmitting station, is rendered difficult and sometimes impossible to amplify, detect, and render audible.

lf means are provided for maintaining the aforesaid radio frequency vacuum tube just below the oscillation point, the tube will pass the desired radio frequency currents at highest efficiency, distant stations will thereby be rendered possible to receive, and nearby stat-ions may be received with greater volume and clarity.

Accordingly the object of the present invention is to provide improved means for maintaining just below the oscillation point a vacuum tube passing high, radio or intermediate, frequency currents.

This object is attained by the use of the improved adjustable radio coils of Nicholas Medved, set forth in his prior application for patent, Serial No. 100,093, and in a companion application for patent, in my improved circuit hereinafter set forth in detail, and which may be stated in general terms as including a primary coil connected between the plate of a vacuum tube and the terminal of a power source, and means connected in parallel with the aforesaid primary coil between the aforesaid plate and power terminal, and which preferably includes a balancing coil having a field opposite the field of the primary, and a preferably variable resistance. Y

` rlhe balancing coil and resistance are connected in series and this series arrangementis connected in parallel with the. primary between the plate and power terminal, and it is found that when the variable resistance is adjusted so that the balancing coil is direct connected between the plate and the power terminahand when the balancing coil and primary each include a predetermined number of turns of wire, that no radio frequency currents whatever' are passed from the plate through the aforesaid radio frequency transformer.

lf, however, the variable resistance is adjusted to connect in series as aforesaid ,with the balancing coil, a resistance whose magnitude is determined by t-he frequency vof the radio frequency currents desired to be passed through the aforesaid primary, the radio frequency vacuum tube may thus be set and maintained in the. desired condition just below the oscillation point, whereby the tube will pass the desired radio frequency currents therethrough at highest efficiency, and whereby distant stations may thus be received, or

nearby stations may be received with greater ceiving sets and in other circuits which will be apparent to persons skilled in the art.

The improved -radio frequency broadcast receiving circuit diagrammatically illustrated in the figure of the drawing, may include an antenna A which may be connected to one terminal of a condenser C1, the other terminal of which is connected to the midpoint of an auto-transformer T1, which preferably includes a conical coil T12, and a conical coil Tlb, adjustable with respect to each other and preferably constructed in detail according to one of the several disclosures of the aforesaid prior application of Nicholas Medved, Serial No. 100,093, or of his comp-anion application for patent for radio coils.

The outer terminal of the coil Tlb, may be grounded as indicated, and the outer terminal of the coil T12, may be connected to the grid' G1 of a radio frequency vacuum tube V1, and the outer terminal of the coil T1a may be also connected to one terminal Cla of a variable triple condenser C1.

The plate P1 of the radio frequency vacuum tube V1, is connected to one terminal of the preferabl conical primary T2-P of an adjustable ba ancing radio frequency transf0rmerT2, preferably of a form illustrated in the companion application of Nicholas Medved for patent for radio coils. The other terminal of the primary T2--P, is connected to the positive terminal of a source of power' as a battery B.

In parallel with the primary T22-13, a balancing coil 'F2-B has one terminal connected to the plate l?, of the radio frequency vacuum tube V1, and its other terminal connected to a terminal of the preferably variable resistance Rb, the other terminal of the resistance Rb being' connected to the positive terminal of the battery B, and a condenser C2 being preferably connected across the terminals of the variable resistance Rh.

In addition to the conical primary T2-P, and the balancing coil T2-B connected as aforesaid, the adjustable balancing radio frequency transformer' T2 includes an adjustable split secondary T2-S made up of one conical coil T2---Sa series connected with another conical coil T2 Sb, the coils T2 Sa and T2- Sb being axially movable with respect to each other, and the transformer T2 being preferably constructed according to the disclosure. of Nicholas Medved in his companion application for patent for radio coils.

While the split secondary of the first adjustable radio frequency transformer T2 may 'be connected directly with a detector tube,

it is preferred to employ a second stage of radio frequency amplification, and for this purpose the outer terminal of the coil T2--Sa is connected with a second terminal Clb of the variable triple condenser C1, and with the grid G2 of a second radio frequency vacuum tube V2.

The plate P2 of the radio frequency vacuum tube V1 is connected to one terminal of the preferably conical primary T2-P of an adjustable balancing radio frequency transformer T2 similar to the transformer T2, and preferably of a form illustrated in the companion application of Nicholas Medved for patent for radio coils. The other terminal of the primary F2-P is connected to the positive terminal of the battery B.

In parallel 'with the primary T2--P, a balancing coil TSHB has one terminal connected to the plate P2 of the radio frequency vacuum tube V1, and its other terminal connected to the terminal of the preferably variable resistance Rb, which is connected to the terminal of the primary T2P, the other terminal of the resistance Rb being connected as aforesaid to the positive terminal of the battery B and the condenser C2 being` preferably connected across the terminals of the variable resistance Rb.

In addition to the conical primary Tg-P and the balancing coil T2-B connected as aforesaid, the adjustable balancing radio frequency transformer T3 includes an adjustable split secondary T2-S made up of one conical coil TS-Sa series connected with another conical, coil Tg-Sb, the coils T2-S2 and Tg-Sb being axially movable with respect to each other and the transformer T3 being preferably constructed according to the disclosure of Nicholas Medved in his companion application for patent for radio coils.

The outer terminal of the coil T-Sa may also be connected with a third terminal C1,1 of the variable triple condenser C2.

The outer terminals of the coilsI T12, T2-Sb, and 'lL-Sb are all connected with each other, and with the common opposite terminal Gld for the aforesaid three separate terminals C12, C11), and C1@ of the triple condenser C1.

he outer terminals of the coils T11), T2-SlJ and Tor-Sb are likewise connected with ground as indicated and `with the negative terminal of a source of power which may be a battery A, the positive terminal of which is connected to the negative terminal of the battery B.

yThe vacuum tubes V1, V2, and V3 are each provided in the usual manner with the lilaments F1, F2, and F3, the negative terminals 1 of which are connected to the negative terminal of the battery A, and the positive terminals of which are connected with the positive terminal of the battery A, and there may be provided a fixed resistance lf3 in series with the negative terminal of the filament F3 and the negative terminal of the battery A, and a variable resistance Rlm in series with the negative filaments F1 and F2 and with the negative terminal of the battery A.

A fixed condenser C4 may be connected between the positive terminal of the filament F2 and the positive terminal of the battery B; and a fixed condenser C2 may likewise be con,- nected between the positive terminal of the filament F2 and the positive terminal of the battery B.

A suitable telephone receiver L may be connected in series between the plate P2 of the detector vacuum tube V3, and a positive terminal of the batte-ry B which may be provided with a plurality of positive terminals for delivering a plurality of different voltages, and a condenser C, may be connected across the terminals of the telephone receiver.

It is to be understood however, that the detector tube V3 may be -connected in a usual manner with any desired radio frequency amplification device before the detected os oillations are passed through a telephone receiver.

For purposes hereinafter to be set forth in detail, it is preferred that the plate 132 be connected with one end of the primary coil 'F2-P and with the opposite end o-f the balancing coil T2-B, whereby the fields of the same are opposed. When conical coils are used as illustrated, the plate P, may be connected to the apex end of the coil T2-P and to the base end of the coil 'F2-B. f

Likewise the plate P2 of the vacuum tube V2 is preferably connected to the apex end of the coil T3-P and with the base end of the coil 'F2-B.

A resistance R4, is preferably connected between thel grid G3 of the detector tube V3 and the connected positive and negative terminals of the battery A and B.

The improved radio frequency broadcast receiving' circuit arranged and connected as aforesaid, has a relatively great selectivity in receiving the broadcast oscillations of a desired transmitting station which may be on the air simultaneously with a number of other transmitting stations, and this high degree of selectivity of the improved circuit is combined with the capability of delivering from the telephone receiver the desired sounds in a. relatively great volume.

The combined -characteristics of a. high degree ofselectivity and great volume of the foregoing circuit, is due in part to the fact that by the proper operation of the set, the radio frequency vacuum tubes are maintained just below the oscillation point at the condition o-f greatest efficiency for passing the desired radio frequency currents..

The filament current of the radio frequency tubes is controlled as aforesaid by the variable resistance itl-2. i

rlhe circuit as a whole is first broadly tuned to approximately the desired frequency by operation of a usual single control forthe triple condenser C1. Y

T he radio frequencyvacuum tubes are then adjusted for operation at highest elliciency, by adjustingthe variable resistance Bim it being understood that when the parallel balancing coils and primary coils ofthe radio frequency transformers are connected directly from the plates of the radio frequency vacuum tubes to the battery, no radio frequency currents pass vbecause of the equal opposed fields. of the balancing coils and the primaries, assuming that the same include equal numbers of turns of wire arranged inl the same way, or the equivalent.

l/Vhen a resistance, depending upon the approximate frequency to which the set as a whole is tuned, is placed in series with the balancing coil or coils, a relatively small resultant field is set up between the balancing 'coils and the primaries, of such nature that any and all charges received upon the plates of the radio frequency vacuum tubes are passed therefrom through the aforesaid coils between the plates and the battery, and whereby the plate is thereby prevented from being overloaded and from setting up the objectionable oscillations or squeals.

After the receiving circuit as a whole has been approximately tuned to the 'desired frequency by operation of the triple condenser C1, and the radio frequency vacuum tubes have been adjusted for operating at the highest efficiency by adjusting the variable resistance Rb, very fine adjustments in the frequency passed by the radio frequency vac uum tubes may be made by adjusting the longitudinal distance between the component coils of the split secondaries 'lf2-S and TB-S.

l claim:

l. An electrical circuit including a vacuum tube and a source of electromotive force, one inductance connected between the plate of the vacuum tube and a terminal of the source of electromotive force, and a second inductance connected in series with a resistance between the plate and the terminal.

2. An electrical circuit including a vacuum tube and a source of electromotive force, one inductance connected between the plate of the vacuum tube and a terminal of the source of electromotive force, and a' second inductance connected in series with a variable resistance between the plate and the terminal.

3. .An electrical circuit including a vacuum tube and a source of electromotive force, one inductance adapted for creating a field of one vdirection and connected between the plate of the vacuum tube and a terminal of the source of electromotive force, and a second inductance adapted for creating a field of a direction opposite to the direction of the field of the first inductance, the second inductance being connected in series with a resistance between the plate and the terminal.

4. An electrical circuit including' a vacuum tube and a source of electromotive force, one inductance adapted for creating a field of one direction and connected between the plate of the vacuum tube and a terminal of the source of electromotive force, and a second inductance adapted for creating a field of a direction opposite to the direction of the ield of the first inductance, the second inductance being connected in series with a Variable resistance between the plate and the terminal.

5. An electrical circuit including a Vacuum tube having a plate, a source of electromotive force for the plate, inductances connected in parallel with each other and between the plate of the vacuum tube and a terminal of the source, and a secondary circuit coupled with the inductances.

6. Electrical apparatus including a Vacuum tube having a plate, a source of electromotive force for the plate, and a plurality of inductances and a resistance connected in parallel with each other and between the plate of the vacuum tube and a terminal of the source, and a secondary circuit coupled with the inductances.

In testimony that l claim the above, I have hereunto subscribed my name.

WALTER MEDVED.

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